Earth-Science Reviews 99 (2010) 99–124 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev The Late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system Edgardo M. Latrubesse a,⁎, Mario Cozzuol b, Silane A.F. da Silva-Caminha c, Catherine A. Rigsby d, Maria Lucia Absy c, Carlos Jaramillo e a University of Texas at Austin-Department of Geography and the Environment, A3100, Austin TX, 78712, USA b Universidade Federal de Minas Gerais, ICB, Departamento de Zoologia, Belo Horizonte, Brazil c Universidade Federal de Mato Grosso, Departamento de Geologia, Cuiabá, MT- 78060-900, Brazil d East Carolina University, Department of Geological Sciences, Greenville, NC, USA e Smithsonian Tropical Research Institute, Balboa, Panama article info abstract Article history: On the basis of paleontological content (vertebrates and palynology) and facies analysis from river banks, road Received 26 February 2009 cuts, and three wells, we have assigned the uppermost levels of the Solimões Formation in western Amazonia, Accepted 8 February 2010 Brazil, to the Late Miocene. The vertebrate fossil record from outcropping sediments is assigned to the Available online 16 February 2010 Huayquerian–Mesopotamian mammalian biozones, spanning 9–6.5 Ma. Additionally, we present results that demonstrate that deposits in Peruvian Amazonia attributed to Miocene tidal environments are actually fluvial Keywords: sediments that have been misinterpreted (both environmentally and chronologically) by several authors. Amazon basin Amazon River The entire Late Miocene sequence was deposited in a continental environment within a subsiding basin. The Late Miocene facies analysis, fossil fauna content, and palynological record indicate that the environment of deposition was Paleogeography dominated by avulsive rivers associated with megafan systems, and avulsive rivers in flood basins (swamps, Paleoecology lakes, internal deltas, and splays). Soils developed on the flatter, drier areas, which were dominated by fossil vertebrates grasslands and gallery forest in a tropical to subtropical climate. palinology These Late Miocene sediments were deposited from westward of the Purus arch up to the border of Brazil with Solimoes Formation Peru (Divisor Ranges) and Bolivia (Pando block). Eastward of the Iquitos structural high, however, more detailed studies, including vertebrate paleontology, need to be performed to calibrate with more precision the ages of the uppermost levels of the Solimões Formation. The evolution of the basin during the late Miocene is mainly related to the tectonic behavior of the Central Andes (∼3°–15°S). At approximately 5 Ma, a segment of low angle of subduction was well developed in the Nazca Plate, and the deformation in the Subandean foreland produced the inland reactivation of the Divisor/ Contamana Ranges and tectonic arrangements in the Eastern Andes. During the Pliocene southwestern Brazilian Amazonia ceased to be an effective sedimentary basin, and became instead an erosional area that contributed sediments to the Amazon fluvial system. At that time, the lowland fluvial systems of southwestern Amazonia (the Purus, Jurua and Javarí basins) become isolated from the Andes by the newly formed north- flowing Ucayali system and south-east flowing Madre de Dios System. It was during the early Pliocene that the Amazon fluvial system integrated regionally and acquired its present appearance, and also when it started to drain water and sediments on a large scale to the Atlantic Ocean. © 2010 Elsevier B.V. All rights reserved. Contents 1. Introduction ............................................................. 100 2. The Solimões Formation ........................................................ 101 2.1. Sedimentology revisited ..................................................... 105 2.2. Fossil fauna .......................................................... 106 2.2.1. Chronology ...................................................... 106 2.2.2. The vertebrate diversity ................................................ 106 ⁎ Corresponding author. Tel./fax: +1 512 471 5116. E-mail address: [email protected] (E.M. Latrubesse). 0012-8252/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.earscirev.2010.02.005 100 E.M. Latrubesse et al. / Earth-Science Reviews 99 (2010) 99–124 2.2.3. Summary of diet habits of mammals as environmental indication . ........................... 110 2.2.4. Freshwater mollusks and ostracods ........................................... 111 2.3. Palynology ........................................................... 112 2.3.1. Biostratigraphic data .................................................. 112 2.3.2. Paleoenvironmental considerations ........................................... 114 3. Amazonia during the Late Miocene ................................................... 115 3.1. Correlation of the Solimões Formation with others lithostratigraphic units of South America ..................... 115 3.2. The Amazon basin: evolutionary approach ............................................ 116 4. Conclusions .............................................................. 121 Acknowledgments ............................................................. 122 References ................................................................. 122 1. Introduction Campbell et al., 2006. Frailey et al., 1988) with large discrepancies. The only late Tertiary lithostratigraphic unit defined and outcropping in Neogene and Quaternary paleogeographic reconstruction of Ama- western Brazilian Amazonia is the Solimões Formation, which extends zonia has produced many hypotheses and models (eg. Hoorn 1994b; for thousands of square kilometers to the west of Manaus (Fig. 1). Fig. 1. Isopach map of the Solimões Formation (from Maia et al., 1977) showing the main depocenters and structural highs within the basin. Numbered circular areas indicate main areas with fossiliferous, palynological and /or geological data. 1 = Upper Acre river; 2 = Acre river upstream of Rio Branco; 3 = BR 364 from Rio Branco to Sena Madureira; 4 = BR 364 from Sena Madureira to Manuel Urbano and outcrops along the Iaco and Purus rivers; 5 = Upper Jurua River; 6 = Feijó-Tarauacá area; 7 = Madre de Dios basin. See Table 1 for details. Wells are indicated as 1AS-32-AM, 1AS-27-AM 1AS-19-AM and IAS-4a-AM. E.M. Latrubesse et al. / Earth-Science Reviews 99 (2010) 99–124 101 Several names have been assigned to this unit in western Brazilian and Table 1 Peruvian Amazonia through time. Caputo et al. (1971) combined the Main studied areas and localities in south-western Brazilian Amazonia. previously defined Puca, (Steinmann 1929), Solimoes (Rego, 1930) Area Main Geology Fossil Palynoloy Location and Cruzeiro (Oppenheim, 1937) into a single unit defined as the localities fauna Solimões Formation. Recently, the old name Pebas (Gabb, 1869) Upper Acre River Patos X X X 10°55′00″S and applied to tertiary sediments of Peru had been retaken by several 69°55′00″W authors (Hoorn, 2006a, Räsänen et al., 1998, Wesselingh et al., 2002 Barranco da XXX10˚56′25″S and ˚ ′ ″ among others) that extended this nomenclature to sediments of the Elizete 69 45 44 W Calvancante X X – 10055′42 S and Solimões Formation in Brazil. 690 49′53 S Hoorn (1993) studying a well and outcrops from the Solimões and Cachoeira XX– 10°56′22″S and Japurá Rivers in the area close to the border of Brazil with Peru and Bandeiras 69°20′37″W) Colombia (Fig. 1) postulated that marine incursions could have Acre River Preventorio X X – Rio Branco Urban (upstream of Area-left bank reached this part of the Amazon during the middle Miocene. Räsänen Rio Branco city) et al. (1995) proposed that the upper Solimões Formation outcrop- Amapa X –– 9037′17.25 S and ping in Acre indicated the existence of a late Miocene intracontinental 68014′12 W seaway through western Amazonia and suggested that this seaway Murici X – X57′24″S and ′ ″ could have connected the Caribbean Sea with the South Atlantic, 69°44 44 W Niteroi X X X 10°08′14″S/ crossing the Venezuelan/Colombian Llanos to the Paraná basin in 67°48′46″W Argentina and passing along western Amazonia and the Beni–Chaco Purus River Talismã X X – 080 10′ 32.1 S and plain. The seaway proposal was well received by a broad community 700 29′4.1 W of researchers, mainly biologists and paleontologists, as a paleogeo- BR 364 road cuts Several XXIn See Fig. 1 (areas graphic alternative for understanding biogeographic patterns in South from Rio Branco along the analysis 3,4 and 6) to Tarauacá road America (Webb, 1996). The seaway model received some criticism (Hoorn, 1996; Marshall and Lundberg, 1996; Praxton et al., 1996), but no concrete evidence invalidating the model has been presented until uppermost portions of this formation (Santos and Silva, 1976). On the now. Recent papers by Hovikoski et al. (2007a,b) also argue for the basis of such maps, Frailey et al. (1988) postulated the existence of a existence of marine influence in southwestern Amazonia (Peruvian late Pleistocene Amazonas Lake, which they suggested, could have and Brazilian Amazon) and for the existence of an epicontinetal covered all of the Amazon Basin and part of the Orinoco Basin embayment of continental dimensions. (forming a lake larger than the Mediterranean Sea). They also Recently, detailed studies have permitted us to better estimate the hypothesized that the sediments of the Solimões Formation could age of the uppermost